KR19990063663A - Cellular communication system with multiple code rates - Google Patents

Abstract

A method and apparatus for selecting an error correction code rate in a cellular wireless system. Each base station broadcasts the value PP of the power product, which is the product of the transmit power P _BT multiplied by the required receive power P _BR . The mobile unit determines the appropriate transmit power P _MT by measuring the received power P _MR and calculating the PP / P _MR 24. Due to the large channel loss, if the calculation result exceeds the mobile unit's maximum transmit power capacity (25), the mobile unit uses a lower code rate and adjusts the transmit power appropriately (27, 31). Three code rates, 2/3, 1/2, and 1/3, are used depending on the amount of channel loss in the preferred embodiment. The code rate selection may also depend on the amount of data to be transmitted (30, 33, 34). The base station detects the code rate by trying to decode all code rates and selecting the best result.

Description

Cellular communication system with multiple code rates

Forward error correction (FEC) coding techniques are frequently used to provide improved error rate performance in communication channels. FEC coding allows the receiving station to reconstruct the contaminated form of the signal transmitted by the transmitting station. Errors in the original signal are due, for example, to noise, interference that obscures low output signals, weakening of the signal due to terrain characteristics, or Rayleigh (multipath) interference.

FEC coding techniques have been used since the 1960s and have been described in many documents (eg, "Error Correction Coding for Digital Communications" by George C. Clark and J. Bibb Cain: Prenum Publishing Co., 1981). A common feature of FEC coding techniques is that the encoding process increases the total number of bits needed for transmission. The ratio of the total number of bits going into the encoder to the total number of bits to be delivered through the channel is commonly referred to as the "code rate". The lower the code rate, the more bits (including data bits and error correction code bits) must be transmitted.

Increasing the total number of bits to be transmitted means that a wider bandwidth must be available for transmission, or that the rate at which user information is sent on the channel ("data rate") is such that the signal containing the coded data is not coded. It needs to be reduced to the point with the same bandwidth that would have been occupied by the signal.

In general, with all others being the same, using a FEC code with a lower code rate provides better correction performance. Thus, for very poor channels, it may be desirable to use very low code rates to achieve acceptable error rate performance. For good channels, very low code rate error correction performance is not needed. In this case, higher code rates provide adequate error rate performance with lower transmit code bit rates, thus higher data rates. Thus, in such a situation, it is more desirable to use higher code rates, especially for systems with a fixed effective bandwidth.

In many communication systems, such as satellite systems, the signal level at the receiver varies relatively from site to site and over time. The primary concern of the designer of such a system is often the power required to be delivered over the link, and bandwidth may be less important. The system designer will choose a single low code rate and, if properly chosen, this one code rate will provide adequate performance in most cases without wasting resources.

However, in terrestrial mobile wireless communications, the signal at the receiver varies widely depending on the distance from the base station to the mobile unit, the presence of terrain features that can weaken the signal, and the fading due to the Rayleigh effect. To change. The channel is fixed within the bandwidth, so the use of FEC coding reduces the amount of talk on the channel. On the forward link (from the base station to the mobile unit), increasing the transmitter power is sometimes only cost effective to ensure that the received signal level is adequate and that the code rate can remain relatively high. . On the reverse link, because of the need to minimize power consumption for long battery life, and because of the potential health risks from placing a high-power microwave transmitter in close proximity to the human body, the mobile unit is capable of transmitting power performance. Frequently also is extremely limited. In many situations, the power level on the forward link is sufficient for the mobile unit to receive well, but the error rate on the reverse link is unacceptable because the power received at the base station is insufficient. Using a lower code rate sometimes solves this problem, but only at the expense of reducing the system's call volume.

Accordingly, there is a need for an improved method of using forward error correction in cellular digital data wireless communication systems. The present invention provides this improvement.

TECHNICAL FIELD The present invention relates to cellular wireless communication systems, and more particularly to methods and apparatus for using multiple code rates for forward error correction in cellular digital data wireless communication systems.

1 is a block diagram illustrating a conventional prior art cellular wireless communication system.

2A and 2B are flow charts illustrating a preferred method of selecting a code rate for a mobile unit in accordance with the present invention.

3A is a block diagram of a first embodiment of a forward error correction code encoder that may be used in the present invention.

3B is a block diagram of a second embodiment of a forward error correction code encoder that may be used in the present invention.

3C is a block diagram of a third embodiment of a forward error correction code encoder that may be used in the present invention.

The present invention includes a method and apparatus for using a plurality of code rates for forward error correction in a cellular digital data wireless communication system. Each base station broadcasts an amount called a power product (PP), which is equal to the base station transmit power P _BT [W] multiplied by the desired received power level P _BR watts [W] at the base station. In order for the mobile unit to determine the appropriate transmit power P _MT [W], it is simply necessary to measure the received power P _MR [W] at the mobile unit and calculate the following equation.

P _MT = PP / P _MR

When channel conditions, such as distance or shadowing, increase the channel path loss, the power control calculation is able to return a value greater than the maximum transmit power capacity of the mobile unit. In this case, the power received at the base station is lower than desired and the final error performance may be difficult to accept. Thus, under the new system, when the mobile unit determines that the desired transmit power level exceeds its capacity, the mobile unit can select a lower code rate. As the code rate decreases, the base station receiver sensitivity improves, and the result is similar to increasing transmitter power.

In the preferred embodiment, the present invention uses three different code rates. Each is based on a convolutional code of constraint length 7 which is standard in the industry. In most cases, the code rate used is a 2/3 rate, but when determining that a larger transmit power is needed than the mobile unit can provide, the code rate changes to 1/2, and in severe cases the code rate Changes to 1/3

Another aspect of the present invention is that the code rate selection of the mobile unit may be based on the amount of data to be transmitted, and by attempting to decode all code rates and selecting the best result, the base station determines the code rate used by the mobile unit. Can be determined.

The main advantages of the present invention are that (1) mobile units with most adverse conditions in mobile wireless data communication systems can achieve acceptable reverse link error performance through the use of very low code rates, (2) All transmissions of a mobile unit that do not have an adverse condition include the majority of transmissions in a cellular wireless communication system, without incorporating capacity degradation resulting from low code rates.

The details of preferred embodiments of the invention are set forth in the accompanying drawings and the description below. Once the details of the present invention are known, many additional technical innovations and changes will be apparent to those skilled in the art.

Like reference numbers and designations in the various drawings indicate like elements.

Throughout the description, the preferred embodiments and examples shown are to be regarded only as examples, and not as a limitation of the present invention.

Principle of operation

The present invention uses a forward error correction technique that a mobile unit can transmit at multiple code rates in a cellular digital data wireless communication system. Since FEC coding is one way to overcome insufficient transmit power capacity in the mobile unit, the selection of the code rate is preferably included in the power control algorithm of the mobile unit. In a preferred embodiment, the power control algorithm is based on the method used in the Cellular Digital Packet Data (CDPD) standard. This method has the advantage that the forward link and reverse link path losses are about the same on average. The forward link path loss can be determined by dividing the base station transmit power P _BT [W] by the power P _MR [W] received at the mobile unit. The reverse link path loss is equal to the mobile unit transmit power P _MT [W] divided by the power level P _BR [W] received at the base station. If these two path losses are set equal to each other and the results are processed, the following equation is obtained.

P _MT = P _BT * P _BR / P _MR

Thus, if the mobile unit can determine the base station transmitter power and can estimate the power level that the mobile unit itself receives, it can also determine what power level the base station receives for performance that the mobile unit can accept. If so, the mobile unit can determine the required mobile transmit power. In the CDPD standard, each base station broadcasts an amount called power product (PP) equal to P _BT * P _BR . In order for the mobile unit to determine the appropriate transmit power, it simply requires measuring the power received at the mobile unit and performing a simple calculation. Thus, the system of the present invention determines whether the transmitted error-corrected encoded data is satisfactorily received by the base station, and if not, a lower code rate is selected for use by the mobile unit. .

When channel conditions, such as distance or shadowing, increase the channel path loss, the power control calculation is able to return a value greater than the maximum transmit power capacity of the mobile unit. In this case, the power received at the base station is lower than desired, and the final error performance may be difficult to accept. Thus, under the system of the present invention, when the mobile unit determines that the desired transmit power level exceeds its capacity, the mobile unit can select a lower code rate. Base station receiver sensitivity improves as the code rate decreases, and the result is similar to increasing transmitter power.

In the preferred embodiment, the present invention uses three different code rates. Each is based on a rising sign of constraint length 7, which is standard in the industry. In most cases, the code rate used is a two-thirds ratio, but when determining that more transmit power is needed than the mobile unit can provide, the code rate changes to half, and in severe cases the code rate Changes to 1/3 Each of these codes is easily decoded at the base station using a single chip decoder (eg, a QUALCOMM Q1650 integrated circuit). The number of code rates, the precise FEC codes used, and the correct choice of the selected rates are not a limitation of the present invention. For example, the FEC code can be selected from Reed Solomon code, BCH code, Hamming code, and other FEC code, or a combination thereof.

In general, overall system capability is a major performance issue, so it is desirable to keep the code rate as high as possible in most situations. In a preferred embodiment, the data is organized in blocks (preferably approximately 400 bits each). Therefore, there are times when separate bits are valid within a block because the data to be delivered is inappropriate to fill the block. Thus, it may be possible to use a lower code rate and still fill all the data in the same number of blocks required for the higher code rate. Therefore, a lower code rate can be selected and the same power level as required for the higher code rate can be used. This may result in performance in excess of what is required, or alternatively, the transmit power may be reduced to provide the same performance that can be achieved with higher code rates, resulting in less battery consumption for the mobile unit, and Reduce the amount of RF interference caused by transmissions in other cells.

Since the rising sign works best when the errors are not correlated, a means of uncorrelating the errors resulting from fading (which may not be necessary for other types of code) is useful. In a preferred embodiment, an interleaver is used to uncorrelate data to be transmitted in a known manner. In a preferred embodiment, the interleaver used is a 20x20 row-column interleaver (although other sizes and other interleaving methods may be used).

In a preferred embodiment, the reverse link message is sent in a manner similar to the CDPD standard, where the message begins with a dotting sequence following the synchronization word and other header bits, and then one column for many blocks is controlled. It is inserted as a bit. The power level and code rate are well chosen at the beginning of the message transmission and do not change during transmission. Each block is encoded independently, using a common code "tailing" technique or a bit flushing technique, to apply a rising code to data having a block structure.

In a preferred embodiment, the base station can determine the code rate of the incoming message by one of two methods. In the first method, an uncoded bit is provided in the header of each message block representing the code rate. However, these bits are vulnerable to errors due to fading, and the base station may fail to extract the appropriate code rate from these bits. Therefore, a second method is provided wherein each block includes a cyclic redundancy check (CRC) code, which enables the base station to determine whether there are errors remaining in the decoded data. Thus, the base station may attempt to decode the data at each possible code rate, and may select any code rate that leads to a result indicating that there is no error by the CRC. If no code rate leads to an error free block, the message is ignored.

It is not necessary to have a CRC to determine the code rate, and other methods can be used to determine which code rate provides the best output. Some examples of such structures are: (1) observing the decoded metric growth rate at each code rate, while comparing the decoded data with the demodulated data and also selecting the rate that results in the best match. Or (2) re-encode the data coming from the base station decoder using the selected ratio. Another possibility is to use the "color code" field of the CDPD standard. Under the CDPD standard, the first 8 bits of a block are fixed and known in advance. Thus, if one code rate decoding of a received block produces a bit that matches a known pattern, that code rate may be selected.

Details of the preferred embodiment

1 is a block diagram illustrating a conventional prior art cellular wireless communication system. The base station 1 is connected to the mobile unit 2 by wireless transmission via an antenna. The mobile unit 2 has a user interface 10, a protocol stack 11, a media access control (MAC) processor 12, modulation and transmission circuits (connected as shown in known methods). 13), duplexer switch 14, antenna 15, receive and demodulation circuit 16, and power estimation circuit 17.

The system of the present invention can be realized in hardware or software, or a combination thereof. In particular, the calculation of the mobile unit transmit power, the selection of the code rate by the mobile unit, and the base station determination of the code rate of the message received from the mobile unit are performed on the base station of the cellular wireless communication system and the programmable computer processor within the mobile unit. It can be realized as a computer program. When a storage medium or device is read by a computer processor to perform the procedures described herein, in order to configure and operate the computer processor, each computer program is a storage that can be read by a general purpose or special purpose computer processor. Good storage on media or device (eg ROM or magnetic diskette). The system of the present invention may be considered to be realized as a computer-readable storage medium configured with a computer program, wherein the storage medium is specific and predetermined to cause the computer processor to perform the protocol described herein. It is configured to operate as.

2A and 2B are flowcharts illustrating a preferred method of selecting a code rate for a mobile unit in accordance with the present invention. Initially, the mobile unit processing system fetches the data to be transmitted in a known manner (step 21). In the preferred embodiment, the data is formatted in the form of 400-bit blocks. Although the entire block capacity is not needed for a particular message, the entire block is transmitted.

The power product PP is periodically transmitted by each base station 1 in the cellular system and received by all mobile units 2 in the area. The power product PP is based on the premise that all mobile units 2 transmit normally using a code rate of 2/3. The power product PP received from the base station 1 is fetched from the appropriate register or location in the mobile unit 2 (step 22). An estimated value of the power P _MR of the signal received from the base station 1 is obtained by a known method from the power estimation circuit 17 (under the CDPD standard, P _MR is a standard received signal strength measure (RSSI) signal. ) (Step 23). The mobile unit 2 then calculates the nominal transmit power P _MT as the ratio of the power product PP divided by the estimated received power P _MR (step 24). In the preferred embodiment, this calculation is made for each transmission. However, this calculation may be made for each message block.

The nominal transmit power P _MT is compared with the maximum transmit power P _MAX of the mobile unit 2 (step 25). If the nominal transmit power (P _MT ) required is less than the maximum transmit power (P _MAX ), then the mobile unit 2 will encode the message at each of the code rates (2/3, 1/2, and 1/3). Calculate the total number of blocks required. This is done to take advantage of the fact that user data may not fill a complete message block, so that there may be some "slack" in the message block. Thus, one rule that can be applied is that if the total number of blocks is the same as for two code rates, then lower code, in order to provide higher reliability at the same transmit power, without increasing the number of bits transmitted. The rate is chosen (since the entire block is always transmitted). Optionally, the availability of the "loose part" allows for lower transmission at lower code rates in order to save battery life for the mobile unit while maintaining the same error rate performance as using higher transmission power at higher code rates. Enable the use of power. In general, the transmit power, code rate, and error rate may be compromised with respect to each other as desired. In the preferred embodiment, power savings and low code rates are optimized to provide an acceptable error rate. Thus, the total number of blocks for the code rate 2/3 and the code rate 1/3 is compared (step 33). If they are the same, the message is encoded using code rate 1/3, and the transmit power close to the calculated nominal transmit power (P _MT ) minus the bias factor (described below) for code rate 1/3. Is selected (step 27). The encoded message is then well interleaved and transmitted (step 28).

If the comparison in step 33 is not the same, the total number of blocks for code rate 2/3 and code rate 1/2 is compared (step 34). If it is the same, the message is encoded using code rate 1/2, and the transmit power is selected that is close to the calculated nominal transmit power P _MT minus the bias factor for code rate 1/2 (step 31). ). The encoded message is then well interleaved and transmitted (step 28).

If the comparison in step 34 is not the same, the message is encoded using the code rate 2/3 and the transmit power close to the calculated nominal transmit power P _MT is selected (step 35).

If the nominal transmit power (P _MT ) is less than the maximum transmit power (P _MAX ) (step 25), the nominal transmit power (P _MT ) is a ratio 1/2 of the maximum transmit power (P _MAX ) of the mobile unit 2. Is compared with the added bias coefficient (step 26). If the nominal transmit power P _MT required is less than this summation, the mobile unit 2 calculates the total number of blocks needed to encode the message at respective code rates 1/2 and 1/3 (step). 29). The total number of blocks for code rate 1/2 and code rate 1/3 is compared (step 30). If it is the same, the message is encoded using code rate 1/3, and the transmit power is selected that is close to the calculated nominal transmit power P _MT minus the bias factor for code rate 1/3 (step 27). ). The encoded message is then well interleaved and transmitted (step 28).

If the total number of blocks for code rate 1/2 and code rate 1/3 is not the same (step 30), the message is encoded using code rate 1/2, and the code is calculated at the calculated nominal transmit power (P _MT ). The transmit power close to the value obtained by subtracting the bias coefficient for the rate 1/2 is selected (step 31). The encoded message is then well interleaved and transmitted (step 28).

If the nominal transmit power (P _MT ) required is less than the maximum transmit power (P _MAX ) plus the bias factor for ratio 1/2 (step 26), the message is encoded using a code rate 1/3. The transmit power close to the calculated nominal transmit power P _MT minus the bias factor for code rate 1/3 is selected (step 27). The encoded message is then sent (step 28).

Each bias coefficient indicates the expected increase in signal-to-noise ratio for that particular encoding (meaning that the receive power P _BR at the base station can be lower, still achieving the same error rate performance as the higher code rate). In a preferred embodiment, the bias for ratio 1/2 is about 1.5 dB and the bias for ratio 1/3 is about 3 dB. Thus, including such bias coefficients improves the overall performance of the system of the present invention. However, such bias coefficients are not necessary to implement the basic concepts of the present invention.

3A is a block diagram of a first embodiment of a forward error correction code encoder that may be used in the present invention. Input data at a rate of N / 3 bits / second (BPS) is input to the 7-bit register 40. As shown, the contents of register 40 are connected to three exclusive OR circuits C0, C1, and C2. For FIG. 3A, the FEC combination polynomial is as follows.

C0 = X ¹ + X ² + X ³ + X ⁴ + X ⁷

C1 = X ¹ + X ³ + X ⁴ + X ⁶ + X ⁷

C2 = X ¹ + X ² + X ³ + X ⁵ + X ⁷

In a known manner, the outputs of the exclusive OR circuits C0, C1 and C2 are connected to the series-parallel converter 42. The output of the parallel-to-serial conversion circuit is a data stream with a ratio of N.

3B is a block diagram of a second embodiment of a forward error correction code encoder that may be used in the present invention. Input data at the rate of N / 2 bits / second is input to the 7-bit register 40. As shown, the contents of register 40 are connected to two exclusive OR circuits C0 and C1. For FIG. 3B, the FEC combination polynomial is as follows.

C0 = X ¹ + X ² + X ³ + X ⁴ + X ⁷

C1 = X ¹ + X ³ + X ⁴ + X ⁶ + X ⁷

In a known manner, the outputs of the exclusive OR circuits C0 and C1 are connected to the series-parallel converter 42. The output of the parallel-to-serial conversion circuit is a data stream with a ratio of N.

3C is a block diagram of a third embodiment of a forward error correction code encoder that may be used in the present invention. Input data at a rate of 2N / 3 bits / second is input to the 7-bit register 40. As shown, the contents of register 40 are connected to two exclusive OR circuits C0 and C1. For FIG. 3C, the FEC combination polynomial is the same as that of FIG. 3B. In a known manner, the outputs of the exclusive OR circuits C0 and C1 are connected to the series-parallel converter 42. The output of the parallel-serial converter 42 is 4N / 3 bits / second. However, the output of the serial-to-parallel converter 42 is a simple counter circuit 44 that selects only three bits every four bits (ie, ignores every fourth bit) to obtain an output data stream with a ratio N. Is connected to. In the preferred embodiment, the count pattern ignores every one of the bits of C0 (binary 10 selection or "block" pattern) and retains all bits of C1 (binary 11 selection or "block" pattern).

The invention may be used on a forward link of a cellular digital data wireless communication system. That is, by changing the code rate in the forward (outbound) signal from the base station to the mobile unit, a gain in system performance can be obtained. If the link is one-to-one (ie, one mobile unit per base channel), this advantage is clearer, but the present invention may provide an advantage in one-to-many link systems. If the signal level received at the base station is less than the level required for the code rate used, the base station can roughly determine what it is to receive the power level expected by the mobile unit. To determine this, the base station can assume that the mobile unit is transmitting at full power and the base station knows what this maximum power is. The procedure is simple after that. If the power transmitted by the mobile unit is P _MT and the power received at the base station is P _BR (considering the difference in antenna gain for reception vs. transmission), the path loss is calculated as P _MT / P _BR . The power level P _MR received by the mobile unit on the forward channel is therefore P _BT * P _BR / P _MT . The system must be set so that there is a minimum required value of P _MR for each effective code rate. When the base station determines that the power at the mobile unit is too low to select the forward channel code rate, the base station can select a lower code rate for the lower block error rate at the mobile unit receiver.

Optionally, in situations where the link is balanced (ie, receiver performance is approximately equal for both the mobile unit and the base station), the base station can change the code rate when it expects the mobile unit to change the code rate. Thus, the mobile unit will know approximately when the received signal changes the ratio, thus reducing the complexity of the mobile unit.

Optionally, the mobile unit may inform the base station by the message sent that the reception level of the mobile unit is too low for the current coding rate and requires a new code rate. If the mobile unit does not notify that the code rate has changed, it may assume that the message has not been received by the base station and only has to re-send the message until the code rate has changed. The determination of when to request a code rate change may be based on a short duration block error rate, a received power level, a short duration bit error rate, or other characteristic.

Optionally, again, under the assumption that the link is somewhat balanced, the code rate being used in the reverse direction is insufficient, so that the code rate selection for the forward channel is lower than the most recent known code rate used on the reverse link. As indicated by what should be reduced, the base station can use the reverse channel block error rate.

summary

In summary, the main advantages of the present invention are (1) to enable most mobile units with adverse conditions in mobile wireless data communication systems to obtain acceptable reverse link error performance through the use of very low code rates; (2) Includes the majority of transmissions in a cellular wireless communication system, without causing capacity degradation resulting from low code rates to all transmissions of mobile units that do not have adverse conditions. Some of the unique features of the present invention,

(1) variable rate coding used in the reverse link of a mobile wireless data communication system,

(2) mobile unit code rate selection integrated in mobile power control, to provide a minimum acceptable performance level at the base station;

(3) mobile unit code rate selection based on the amount of data to be transmitted;

(4) Base station determination of the code rate by attempting to decode all code rates and selecting the best result.

A number of embodiments of the invention have been described. Nevertheless, it should be understood that many modifications may be made without departing from the spirit and scope of the invention. For example, a method and algorithm for selecting a code rate may be based on (1) receive (forward) channel block error rate, (2) based on transmit (reverse) channel block error rate, and (3) It can be based on the re-transmission rate in the link, and (4) can be calculated by the base station from the known characteristics of the mobile unit, and the measurement of the channel between the base station and this mobile unit, and then transmitted to this mobile unit. As another example, only two code rates may be used, or three or more code rates may be used. Moreover, as will be appreciated in the art, the order in which the steps of FIGS. 2A and 2B are shown may be varied in many cases without affecting the outcome of the procedure. As another example, the present invention can be used on a forward link as well as a reverse link in a communication system. Accordingly, it is to be understood that the invention is not limited by the particular embodiments shown, but only by the scope of the appended claims.

Claims (18)

A method for improving transmission performance in a cellular digital data wireless communication system, (a) transmitting the error-corrected encoded data from the mobile unit to the base station using the first code rate; (b) determine whether the error-corrected encoded data transmitted using the first code rate is satisfactorily received by the base station; otherwise, for the mobile unit, the first code rate Selecting a lesser second code rate, (c) transmitting error-corrected encoded data from the mobile unit to the base station using the second code rate. The method of claim 1, (a) determining whether the error-corrected encoded data transmitted using the second code rate is satisfactorily received by the base station; otherwise, for the mobile unit, the second code Selecting a third code rate less than the rate; (b) transmitting error-corrected encoded data from said mobile unit to said base station using said third code rate. The method of claim 1, (a) determining, at the base station, the code rate for error-corrected encoded data received from the mobile unit, attempting to decode such data using all possible code rates valid for the mobile unit. Determining and selecting the code rate that best decodes such data. The method of claim 1, (a) interleaving the error-corrected encoded data prior to transmission from the mobile unit. A method for improving transmission performance in a cellular digital data wireless communication system, the method comprising: (a) determining a transmit power level required for the mobile unit to transmit data from the mobile unit to the base station; (b) determining whether the required transmit power level is less than the maximum transmit power level of the mobile unit, (1) if so, select a first code rate for error-correcting encoding such data and a first transmit power level that is less than or equal to the maximum transmit power level of the mobile unit, and wherein the first Transmitting the error-corrected encoded data from the mobile unit to the base station using the code rate and the first transmit power level of; (2) If not, a bias associated with the second code rate from the maximum transmit power level of the mobile unit and a second code rate less than the first code rate for error-correcting encoding such data. Select a second transmit power level that is less than or equal to a factor that is less than the subtracted value and use the second code rate and the second transmit power level to obtain error-corrected encoded data from the mobile unit. Transmitting to the base station. The method of claim 5, wherein the data is transmitted in blocks, wherein the method comprises: (a) if the required transmit power level is less than the maximum transmit power level of the mobile unit, the number of blocks required to transmit such data is equal to the second code rate, as for the first code rate. If the same is true for the transmission rate, selecting the second code rate. The method of claim 5, (a) determining, at the base station, the code rate for error-corrected encoded data received from the mobile unit, attempting to decode such data using all possible code rates valid for the mobile unit. Determining and selecting the code rate that best decodes such data. The method of claim 5, (a) interleaving the error-corrected encoded data prior to transmission from the mobile unit. A method for improving transmission performance in a cellular digital data wireless communication system, the method comprising: (a) determining a transmit power level required for the mobile unit to transmit data from the mobile unit to the base station; (b) determine if the required transmit power level is less than the maximum transmit power level of the mobile unit, and if so, a first code rate for error-correcting encoding such data and the maximum transmission of the mobile unit; Selecting a first transmit power level that is less than or equal to a power level, and using the first code rate and the first transmit power level, error-corrected encoded data from the mobile unit to the base station; Transmitting, (c) if not, determine whether the required transmit power level is less than the maximum transmit power level of the mobile unit plus a first bias coefficient associated with a second code rate, and if so, such data The first bias coefficient is less than or equal to the second code rate less than the first code rate and the first bias coefficient is subtracted from the maximum transmit power level of the mobile unit for error-correcting encoding. Selecting a second transmit power level and transmitting error-corrected encoded data from the mobile unit to the base station using the second code rate and the second transmit power level; (d) if not, associated with the third code rate from the maximum transmit power level of the mobile unit and a third code rate less than the second code rate for error-correcting encoding such data. Select a third transmit power level at which the second bias coefficient is less than or equal to the subtracted value, and use the third code rate and the third transmit power level to obtain error-corrected encoded data; Transmitting from the mobile unit to the base station. 10. The method of claim 9, wherein data is transmitted in blocks, wherein the method comprises: (a) if the required transmit power level is less than the maximum transmit power level of the mobile unit, (1) if the number of blocks required to transmit such data is the same for the third code rate, such as for the first code rate, selecting the third code rate; , (2) if the total number of blocks required to transmit such data is the same for the second code rate, as for the first code rate, further comprising selecting the second code rate The transmission performance improvement method characterized by the above-mentioned. 10. The method of claim 9, wherein data is transmitted in blocks, wherein the method comprises: (a) if the required transmit power level is less than the maximum transmit power level of the mobile unit plus the first bias coefficient; (1) if the number of blocks required to transmit such data is the same for the third code rate, as for the second code rate, further comprising selecting the third code rate The transmission performance improvement method characterized by the above-mentioned. The method of claim 9, (a) determining, at the base station, the code rate for error-corrected encoded data received from the mobile unit, attempting to decode such data using all possible code rates valid for the mobile unit. Determining and selecting the code rate that best decodes such data. The method of claim 9, (a) interleaving the error-corrected encoded data prior to transmission from the mobile unit. A system for improving transmission performance in a cellular digital data wireless communication system, the system comprising: (a) a wireless transmission system for transmitting error-corrected encoded data from a mobile unit to a base station, (b) connected to the wireless transmission system, (1) for error-correcting encoding of this data, select a first code rate for the mobile unit, (2) if the error-corrected encoded data transmitted using the first code rate is not satisfactorily received by the base station, then for error-correcting encoding such data, than the first code rate. And a selector for selecting a second code rate for the mobile unit. 15. The system of claim 14, further comprising an interleaver for interleaving error-corrected encoded data prior to transmission from the mobile unit. The system of claim 14, wherein data is transmitted in blocks, wherein the system comprises: (a) determine if the number of blocks connected to the selector and required to transmit such data is the same for the second code rate, as for the first code rate, and if so, the selector And a comparator for selecting the second code rate in preference to the first code rate. A computer program for improving transmission performance in a cellular digital data wireless communication system, Each computer program, when read and executed by a computer processor, is executed by the computer processor, (a) transmitting error-corrected encoded data from the mobile unit to the base station using the first code rate; (b) determine whether the error-corrected encoded data transmitted using the first code rate is to be satisfactorily received by the base station; otherwise, determine the mobile unit less than the first code rate. Function to select a second code rate for (c) using said second code rate, stored on a readable medium by a computer processor to perform a function of transmitting error-corrected encoded data from said mobile unit to said base station. Computer program to improve transmission performance. In a computer-readable storage medium composed of a computer program, The storage medium is configured such that the computer processor operates in a specific and predetermined manner so that the computer processor (a) transmitting error-corrected encoded data from the mobile unit to the base station using the first code rate; (b) determine whether the error-corrected encoded data transmitted using the first code rate is to be satisfactorily received by the base station; otherwise, the mobile unit is less than the first code rate. The ability to select a second code rate for (c) using the second code rate to perform the function of transmitting error-corrected encoded data from the mobile unit to the base station.